(1) Field of the Invention
The present invention relates to a flame-retardant polyolefin foam and more particularly to a polyolefin foam which is flame-retardant and superior in thermoformability.
(2) Description of the Prior Art
As the prior art concerning a flame-retardant polyolefin foam, there is known the art in which 5-30 parts by weight of a halogen-containing flame retardant and 50-500 parts by weight of a hydrated metal oxide are added to 100 parts by weight of an ethylene-vinyl acetate copolymer resin (EVA resin) and the resulting composition is crosslinked and foamed, as shown in U.K. Laid-Open Patent Application GB 2070021A.
In the above prior art process, however, since the amount of additives added to the base resin, such as a flame retardant, a hydrated metal oxide, etc., is as large as 60 to 580 parts by weight based on 100 parts by weight of the base resin, the strength and elongation and thermoformability of the resultant foam are deteriorated, although a superior flame retardancy is obtained.
In general, from the standpoint of thermoformability, the larger the amount of additives, the less desirable as explained above, and if the compatibility and adhesion between additives and a base resin are poor, both may come off at their interface, the escape of gas evolved from a blowing agent is likely to occur and coarse cells are easily formed, during heat-foaming. As a result, the obtained foam is inferior in tensile strength and tensile elongation and in formability.
The present inventors succeeded in obtaining a polyolefin foam superior in both flame retardancy and thermoformability by incorporating 2 to 10 wt. % (as bromine content) of a bisphenol A-based brominated epoxy resin or a crosslinked product thereof which are highly compatible with polyolefins as a flame retardant, into the polyolefin foam, and by also incorporating or not incorporating therein 0 to 25 wt. % of an inorganic filler, the inorganic filler thus being not used at all or being used in a small amount. Such a polyolefin foam superior in both flame retardancy and thermoformability has not been known.